There are different type of smd capacitor ; the one I mainly use are mlcc – multi layer ceramic capacitor. In this technology, there are different dielectric (NP0, X7R, X5R, Y5V) with different characteristics.
I was looking for informations about this and found different nice website. I’ll try to summarize what I found in this post.
The codification is given by a norm depending on the Class and Temperature stability (see wikipedia post in the link below)
As an example, X5R means => max 15% variation in a [-55;+85]°C range.
Equivalent Serial Resistor is low for Ceramic capacitor with 0.01 to 0.1 ohm compared to 2-30 ohm for aluminium capacitor or 1-2 ohm for tantalum. Low ESR version of aluminum reach 1-5 ohm and low ESR version of tantalum reach 0,05 – 1 ohm
Ceramic have a 10x factor compared to other technologies ; that’s why we do not have a lot of information about ESR in the ceramic documentation, it is because they are low 😉
NP0 / C0G
NP0 / C0G is the best dielectric but having a small dielectric constant – and so requiring more space. The temperature do not really have an impact on the capacitance as voltage and age. The capacitance is really stable.
The maximal capacitance on SMD is about 10nF with 1206 package.
X7R is a compromise with a dielectric constant from 2000 to 4000, it is sensitive to environment but in a reasonable slot.
- Temperature impacts capacitance less than 10% ; about 5% in [-55;+75]°C
- Voltage decrease the capacitance
- Time is decreasing capacitance about 2.5% per decade hour.
Voltage impacts the capacitance up to 20% of the nominal value ; using a capacitor of 10V for a 5V usage will limit the impact about 10% (personal estimate)
X7R allow up to 10uF/10V – 2.2uF/25V for 0805 package
Is really near X7R dielectric with lower performance ; the impact of temperature is about 5% for [-20;+60]°C
Voltage impacts the capacitance – it can be up-to 50% even low voltage : a 6.3V 22uF can deliver no more than 12uF once connected to 3V DC. To limit impacts it is important to use Capacitor with really higher voltage than power supply ; it is common to loose 70% of the capacity when reaching the voltage limit.
Up to 10uF in a 0805 package
Y5V allow to have large capacity in a smaller package with a large dielectric constant over 16K but the environment have a large impact on the capacitance :
- Temperature impacts capacitance from 60 to 80% the nominal value. 15% under 0°C and over 40°C
- Voltage also reduce the capacitance ; up to 60% of the nominal value
- Time is decreasing capacitance up to 7% per decade hour (can be canceled by heating over 125°C)
This type of SMT capacitor is not impacted by the voltage and keep a stable capacitance over the voltage.
This link – johansondielectrics – is a good start where the building process is described with the main characteristics for NP0 / X7R / Y5V)
This link – niccomp.com – explains the impact of voltage on capacitance
Some interesting slides from Oracle about Voltage bias
The Wikipedia post on ceramic capacitor with many more details
The Wikipedia post about ESR